ALGAE IN SOME COLORADO SOILS. 
By W. W. Robbins. 
INTRODUCTION. 
It has been experimentally demonstrated by Professor Walter 
G. Sackett (i) that many of the cultivated soils of Colorado possess 
the power to fix free atmospheric nitrogen. This fixation takes 
place in the soils themselves as well as in culture solutions. Azoto- 
bacter chroococcnm is found to be the chief nitrogen fixing organ¬ 
ism. It is now well known that unprecedented quantities of ni¬ 
trates accumulate in certain soils of Colorado, resulting in so-cal!e :1 
“niter areas”; the quantities are such as to kill off not only higher 
types of plants but the nitrogen fixing organisms themselves. The 
evidence brought to light by Dr. W. P. Headden (2), showing that 
the accumulation of these nitrates is not due to seepage or ground 
waters is too clear and certain to admit of dispute. Added to this 
are the results brought forward by Professor Sackett that certain 
of our soils have a high nitrogen fixing power. Naturally, the 
unusual accumulation of nitrates is thought to be due to the fix¬ 
ation of free atmospheric nitrogen by the soils themselves, accom¬ 
panied by ammonification and nitrification. 
As our soils are ooor in organic matter, it seemed difficult to 
account for the source of energy that would be necessary to sup¬ 
port such a rich nitrogen fixing flora. If it could be shown that 
our soils have an abundance of algae present, this condition would, 
at least, be highly suggestive that the energy for Azotobacter was 
being supplied in large part by these chlorophyl-bearing organisms 
Hence it was that, with this in mind, the present preliminary study 
of the algae in our soils was undertaken. 
I am indebted to Professor Sackett for the problem and for 
many laboratory facilities extended to me in the course of this 
study. The soil samples were collected by him. 
HISTORICAL. 
It is well known that certain bacteria and algae enter into a 
symbiotic relationship, in which the latter furnish the bacteria 
with the necessary energy in the form of carbohydrates, while the 
bacteria supply the algae with nitrates. MM. Bouilhac and Guis- 
tiniana (3) showed that Nostoc punctiforme and Anabaena , when as¬ 
sociated with bacteria, grew well on sand supplied with mineral 
nutrients in which nitrogen and organic material were lacking 
Furthermore, the mixture could accumulate enough nitrogen to 
(1) Sackett, Walter G., Bacteriological Studies .of the Fixation of Nitrogen in Certain 
Colorado Soils. Colorado Agricultural Fxp. Sta., Bull. 179, pp. 1-42, 1911. 
(2) Headden, W. P. The Fixation of Nitrogen in Some Colorado Soils. Colorado 
Agricultural Exp. Sta., Bull. 155, pp. 1-48, 1910, and Bull. 178, pp. 1-96, 1911. 
(3) MM. Bouilhac and Guistiniana. Sur une culture de sarrasin en presence d’un melange 
d’algues et bacteries. Compt. rend, de 1’Acad. T. CXXXVII, pp. 1274-1276, 1903. Sur des 
cultures de diverses plantes superieures en presence d’un melange d’algues et de bacteries. 
Comp. rend, de l’Acad. T. CXXXVIII, pp. 293-296, 1904. 
